1. Field of the Invention
The invention relates to vehicle axle/suspension systems, and in particular to the suspension assemblies of those systems which are useful for heavy-duty vehicles such as semi-trailers. More particularly, the invention is directed to heavy-duty suspension assemblies which include a bushing assembly for pivotally mounting one end of the suspension assembly beam to the vehicle frame via a frame hanger, wherein an improved spacer apparatus is disposed between each side of the bushing assembly and the sidewalls of the frame hanger, to generally prevent or minimize relative movement between the bushing assembly and the wear pad or spacer disk of the spacer apparatus, or alternatively to generally prevent or minimize direct contact between substantially non-planar surfaces of the bushing assembly and the spacer disk by increasing the bearing area therebetween, thus generally eliminating excessive wear or damage to the spacer disk and possible resulting damage to the axle/suspension system.
2. Background Art
Air-ride leading or trailing beam-type axle/suspension systems are conventionally utilized on heavy-duty vehicles such as semi-trailers. For the sake of illustration and understanding, an air-ride axle/suspension system having a trailing beam for use on a semi-trailer will be discussed hereinbelow. Each axle/suspension system includes a pair of transversely spaced suspension assemblies each having a trailing beam. Each beam has a generally stiff construction between its front and rear ends without any joints, pivot points, or the like, so that the beam structure itself is free of significant deflection. The stiff arms or beams of most of these types of axle/suspension systems are rigidly attached to the axle at the middle to rear end of the beam opposite from its front end that is pivotally connected to the vehicle frame hanger. Due to this rigid axle-to-beam connection, when the trailer leans from side to side during operation over the road, the axle is subjected to torsional forces. In addition, the rigid beam construction combined with the rigid axle-to-beam connection means that those torsional axle forces are transmitted forward through the beam and into rotational, fore-aft, side, and vertical movement at the pivotally attached front end of the beam.
As noted hereinabove, the beam-to-frame hanger pivotal attachment is accomplished by a bushing assembly typically comprising an elastomeric bushing which is molded around and adhesively attached to a central steel sleeve having a continuous passage formed therethrough. The elastomeric bushing in turn is press fit into a robust steel mounting tube. The entire bushing assembly is securely attached to the other components of the beam to complete the beam structure. Conventional fasteners then are used to pivotally attach the bushing assembly to the frame hanger.
Also, it is well known in the suspension art and literature that the elastomeric bushing can be designed to different specifications, thereby customizing its deflection rate which in turn dictates the amount of trailer lean that can occur for a given roll movement during operation of the vehicle. More specifically, in the above-described types of axle/suspension systems, the elastomeric bushing typically is engineered to deflect a greater amount in the vertical direction than in the fore-aft direction to allow a desirable amount of trailer lean which is neither too large or too small, while at the same time preventing excessive fore-aft movement that could cause the axle to steer off from a straight tracking condition. The larger vertical bushing deflection also assists in preventing excessive stress build-up at the rigid axle-to-beam connection which could result from the axle torsional forces, but which instead are reacted by the trailing beam through the bushing deflections. One example of this class of elastomeric bushings which deflect a larger distance in the vertical direction than in the fore-aft direction are the TRI-FUNCTIONAL (a federally registered trademark of The Boler Company) bushings, which are marketed by The Boler Company. In the described types of axle/suspension systems, the vertical movement at the point of attachment of the bushing assembly to the vehicle frame hanger can be up to about 0.75 inches in either vertical direction, and rotational movement can be as large as about 30° (thirty degrees). Such movement amounts are significant.
The pivotal connection of the suspension assembly to the frame hanger also is the location of significant side loads. Such side loads typically occur when the trailer is turning and/or its tires rub against a curb, causing side loads to be imposed on the axle. This pivotal connection via the bushing assembly is the only attachment point between each suspension assembly and the vehicle frame, other than the air spring and the shock absorber. The air spring is mounted on and extends between the rear end of the beam and the vehicle frame, and the shock absorber typically also is mounted on and extends between a selected location on the beam and vehicle frame. However, air springs and shock absorbers do not function to react side loads encountered by the axle. Thus, the above-described bushing assembly is solely responsible for reacting such side loads encountered by the axle/suspension system and its suspension assemblies.
In addition to the sources of side loads described immediately above, many roads around the world, including those in the United States, have a significant road crown to aid drainage. Due to the crown in the road, trailers often lean to the passenger side of the road and may “dogtrack” or steer toward the passenger side or berm of the road. In a trailing arm axle/suspension system, such lean to the passenger side can cause the beams to rub against the driver's side of the frame hangers to control the side movement of the axle and keep the axle tracking straight. In addition, many such crowned roads are located in remote areas and consequently sometimes are not properly maintained. Nonetheless, vehicles such as semi-trailers still must haul heavy payloads on such roads and often travel for many hours thereon before encountering well-maintained roads, which can place even more stress on the axle/suspension system.
If the side loads are large enough, and also if the lean to the passenger side severe enough and the road bumpy enough, such a trailing arm might move as much as about 0.75 inches vertically in either direction, pushing hard sideways, and rotating up to 30° (thirty degrees), all concurrently. Such loadings typically will create a significant amount of heat if the robust metal mounting tube of the bushing assembly grinds against the driver's side sidewall of the frame hanger. Of course, depending on the operational situation, such grinding also can occur on the passenger side sidewall of the frame hanger. For this reason, a spacer disk conventionally is used to insulate the opposing steel surfaces of each outer edge of the mounting tube and its respective sidewall of the frame hanger, to prevent the mounting tube from gyrating directly against the stationary frame hanger.
More particularly, a spacer disk is located between each side of the bushing assembly and its respective frame hanger sidewall. The spacer disk typically is made of a suitable plastic material that has excellent durability, such as ultrahigh molecular weight polyethylene. However, such plastic materials have been found to typically deform at about 150° F., and when road conditions are severe enough, as described immediately above, the rotating, deflecting bushing assembly can generate heat reaching temperatures of about 150° F.
In addition, when the vehicle leans, the compliance in the bushing keeps the wheels on the ground at least until a tip over condition would occur. The resulting tilt or lean of each trailing beam in its respective frame hanger causes point loading of the edge of the steel bushing mounting tube against the plastic spacer disk, which in turn contacts the sidewall of the hanger. Such point or line loading is of a high enough force to deform the spacer disk material. If left unchecked, the spacer disk can become excessively worn and too thin to be effective in its insulating purpose. Eventually, the affected spacer disk will tear away and the trailing beam and especially its bushing mounting tube will grind directly into the sidewall of the hanger. The additional heat generated by the grinding steel surfaces can cause the elastomeric bushing to quickly deteriorate, which in turn can cause even more steel-on-steel grinding. If this condition is left unchecked, the suspension beam will rub a groove into the side of the hanger, which can cause the beam to become mechanically locked with the hanger and prevent it from deflecting vertically. Without proper deflection at the beam to frame hanger pivotal connection, high stresses concentrate at the rigid beam to axle connection, potentially reducing the useful life of the beam or axle. At the very least, such damage can cause excessive axle misalignment and steering problems. This type of damage to the frame hanger and/or the axle/suspension system likely would require its replacement. Of course, such damage is undesirable, inconvenient and costly.
One possible solution to the above-described problem might appear to be to increase the temperature stability of the material forming the spacer disk. However, the movement forces and point loading described immediately above, especially in combination with severe road conditions, may be too adverse even for the most advanced material to withstand for the life of the vehicle.
The present invention contemplates combining a load dissipation structure or structures with a conventional spacer disk, to comprise a spacer apparatus of individual components working in cooperation. The present invention further contemplates an integral one-piece spacer apparatus that generally eliminates relative movement between the bushing assembly and the spacer disk. More particularly, one embodiment of the spacer apparatus of the present invention minimizes or prevents the above-described relative movement between the bushing assembly and the spacer disk and transfers that relative motion to movement between the improved spacer apparatus and the frame hanger. This movement relocation significantly reduces the loads between the bushing mounting tube and the spacer disk. Two other embodiments of the present invention increase the bearing area of the material in direct contact with the spacer disk from the relatively thin edge of the bushing mounting tube to a substantially planar area of a load dissipation structure. Thus, in a vehicle roll situation, this greater planar area moves in concert with the bushing assembly and directly contacts the spacer disk, instead of the relatively thin, sharp edge of the mounting tube contacting the spacer disk. This arrangement of parts greatly reduces the force on the spacer disk from a line or point-type of contact force and into more of a flat, dispersed type of force. Thus, even though the temperatures generated by the gyrating bushing assembly still may approach the maximum that the spacer disk material can withstand, excessive wear and resultant damage to the disk will be minimized or eliminated because the forces acting on the disk are dispersed and therefore relatively low at any one point on the disk.
As a result of the improved spacer apparatus of the present invention, the spacer disk can protect the frame hanger, and the suspension assembly can operate in a normal manner without the significant possibility of mechanical lock-up with the frame hanger, and the resulting chance of damage to the hanger and the axle/suspension system.